Fig. 5.

A highly selective and self-powered gas sensor via organic surface functionalization of p-Si/n-ZnO diodes. a Schematic of a singular p-n unit composed of p-Si μ-trenches. b The surface of the n-ZnO NWs was modified by adding a SAM of functional groups. c SEM image of a singular p-Si/n-ZnO diode (scale bar: 10 μm). d Diagram of the ΔV _oc response for different NO₂ concentrations, for amine- and thiol-functionalized devices. e Most stable geometries of NO₂ molecules adsorbed at the thiol and amine functionalities. f Energy levels of the HOMO and LUMO of the functionalities without adsorbed NO₂ and with adsorbed NO₂. The averaged electrostatic potential from the core region of the Si atom of each functionality was used as reference potential. The HOMO level of the isolated thiol functionality was set to 0 for convenience. Figures adapted from [72]